#include<iostream>
#include<string>
#include<vector>

using namespace std;
class Solution {
public:
    void reverseString(vector<char>& s) 
    {
        int begin = 0;
        int end = s.size()-1;
        while (begin < end)
        {
            swap(s[begin], s[end]);
            begin++;
            end--;
        }
    }
};

